When I suggest something to Eloise she has taken to answering with a sentence that starts with 'could be' rather than a simple yes or no.
"Would you like to have some lunch?" she answers, "could be really yummy?"
To "let's go read books in bed," Eloise will say, "could be really cozy."
And sometimes Eloise will suggest that an activity, like chasing the dog, "could be really funny."
Eloise's 'could be' is sometimes a question and sometimes a statement. It is not a phrase that we use, so I'd say it 'could be' something she's come up with all on her own.